Battery cathode

ABSTRACT

A cathode having a groove extending about 10 to about 450 microns into a surface of the cathode. The cathode can also be roughened.

BACKGROUND

This invention generally relates to battery cathodes.

Batteries are commonly used electrical energy sources. A batterycontains a negative electrode, typically called an anode, and a positiveelectrode, typically called a cathode. The cathode may include apositive active material (e.g., a transition metal oxide such as MnO₂)that can be reduced, a conductive aid (e.g., graphite), and a binder(e.g., polyethylene (PE)). The anode can be a gel including an activematerial (e.g., zinc particles) that can be oxidized. The anode activematerial is capable of reducing the cathode active material. In order toprevent direct reaction of the anode material and the cathode material,the anode and the cathode are electrically isolated from each other by aseparator.

When the battery is used as an electrical energy source in a device,electrical contact is made to the anode and the cathode, allowingelectrons to flow through the device and permitting the respectiveoxidation and reduction reactions to occur to provide electrical power.An electrolyte in contact with the anode and the cathode contains ionsthat flow through the separator between the electrodes to maintaincharge balance throughout the battery during discharge.

Alkaline batteries include cylindrical batteries, for example, theconventional AA, AAA, AAAA, C, and D batteries, commonly sold in stores.These conventional alkaline batteries include a cylindrical container(called a can) containing a central, cylindrical gel anode surrounded bya hollow cylindrical transition metal oxide cathode.

A cylindrical cathode can be made by a number of ways. One method is toplace a number of ring-shaped discs in the can to form a tall, loosefitting hollow cylinder. The discs are reformed in the can to providegood contact to the can wall by placing a core rod in the cavity of thecylinder and re-compacting the discs by applying pressure to the top ofthe discs. The discs can also be made oversized, i.e., the outerdiameter of the discs is bigger than the inner diameter of the can, andforce fit into the can by inserting them through a tapered funnel.Another method of making the cathode includes placing cathode powder orgranules in the can and forming the cathode by driving a central corerod into the powder while restraining the powder on the top surface ofthe cathode with a punch. Cathodes made by these methods can have shiny,glazed surfaces with closed pores.

SUMMARY

The invention relates to a battery having a cathode modified by groovingand/or roughening. Generally, the modified battery has good capacity athigh and low drain rates and under continuous and intermittent dischargerates.

Without wishing to be bound to any theories, it is believed thatmodifying the cathode enhances the performance of the battery byincreasing the surface area of the cathode and allowing more electrolyteto be sorbed through open pores on the surface of the cathode. Increasedsurface area and/or electrolyte flux may enhance battery performance bylowering mass transfer resistance in the cathode, lowering separatorpolarization, and/or delaying anode passivation.

In one aspect, the invention features a cathode having at least onegroove extending about 10 to about 450 microns, preferably about 70 toabout 110 microns, into a surface of the cathode. The cathode can beshaped as a cored cylinder having an interior surface and an exteriorsurface, wherein the groove extends into the interior surface of thecathode. The groove may extend helically about the longitudinal axis ofthe cathode or parallel to the length of the cathode. The cathode can beshaped as a prism, and the groove may extend into a major surface of thecathode. The invention also features a battery (e.g., cylindrical,prismatic, and button) having the cathode as generally described above.

In another aspect, the invention features a cathode having a surface andincluding graphite particles at a surface of the cathode. The graphiteparticles may have a-b crystallographic planes oriented substantiallynon-parallel, e.g., substantially perpendicular, to the surface of thecathode. The a-b crystallographic planes of the graphite particles maybe oriented substantially perpendicular to the length of the cathodeand/or substantially parallel to the major axis of the cathode. Thecathode may include a current collector having a major surfaceperpendicular to the a-b planes of the graphite particles. The cathodemay be shaped as a cylinder or a prism. The invention also features abattery (e.g., cylindrical, prismatic, and button) having the cathode asgenerally described above.

In another aspect, the invention features a battery having a cathodehaving at least one groove extending about 10 to about 450 microns,e.g., about 70 to about 100 microns, into a surface of the cathode, asgenerally described above. The cathode may define a cavity and thebattery may include a separator having a cylindrical shape disposed inthe cavity. The battery can be cylindrical (e.g., a AA, AAA, C, D) andcan have a separator shaped as a cylinder.

In another aspect, the invention features a method of making a cathodeand a battery. The method includes forming grooves in the surface of thecathode. The grooves may extend into the surface to a depth of about 10to about 450 microns. Forming the grooves may include contacting athreaded tap with the surface of the cathode, contacting a straightfluted tap to the surface of the cathode, and/or mechanically removing aportion of the surface of the cathode, e.g., by turning or pushing.

In another aspect, the invention features a method of making a batteryincluding forming a cathode having a surface and graphite particles atthe surface of the cathode, wherein the graphite particles have a-bcrystallographic planes oriented non-parallel to the surface of thecathode. The method may further include placing a separator adjacent tothe surface of the cathode.

In another aspect, the invention features a method of making a batteryincluding forming a cathode including graphite particles having a-bcrystallographic planes oriented substantially parallel to a surface ofthe cathode. Forming the cathode may include packing a portion ofcathode material in a can. The method may further include drilling thecathode perpendicularly to the surface of the cathode.

The method can substantially orient the graphite particles such that thea-b planes are parallel to the plane of conduction at the innerdiameter, at the outer diameter, and within the bulk of the cathode forcylindrical cells. This orientation facilitates both electronic andionic conduction in the cathode.

Other features, objects, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side-sectional view of a cylindrical battery;

FIGS. 2A–2B are schematic side-sectional views of cylindrical batterieshaving grooved cathodes;

FIG. 3 is a graph showing cell potential vs. capacity yield for abattery having a grooved cathode;

FIG. 4 is a graph showing cell potential vs. capacity yield for anotherbattery having a grooved cathode;

FIG. 5 is a graph showing closed circuit voltage vs. time for a batteryhaving a grooved cathode;

FIG. 6 is a graph showing electrolyte absorbed vs. time for batterieshaving grooved cathodes;

FIGS. 7A–B are graphs showing anode passivation vs. capacity for cellswith grooved cathodes, under galvanostatic and galvanodynamic discharge,respectively;

FIGS. 8A–B are graphs showing polarization (Ohmic and kinetic, and masstransfer, respectively) vs. pulse current for cells with groovedcathodes;

FIG. 9 is a graph showing cell polarization vs. pulse current for cellswith grooved cathodes;

FIG. 10 is a diagram illustrating an atomic structure of graphiteparticles;

FIG. 11 is a diagram illustrating a possible effect of grooving orroughening on the surface of a cathode;

FIG. 12 is a side-sectional view of a prismatic battery; and

FIG. 13 is a perspective view of a button or coin battery.

DETAILED DESCRIPTION

The invention relates to a battery cathode having a surface thatenhances the performance of the battery.

Referring to FIG. 1, battery 10 includes a cathode 12, an anode 14, aseparator 16 and a cylindrical can 18. Battery 10 also includes acurrent collector 20, a seal 22, and a metal top cap 24, which serves asthe negative terminal for the battery. The cathode 12 is in contact withthe can 18, and the positive terminal of the battery is at the oppositeend of the battery from the negative terminal. An electrolytic solutionis dispersed throughout battery 10. The invention described herein canbe applied to batteries of different sizes, but for purposes of theembodiment described below, battery 10 is a AA battery.

Cathode 12 includes an active material, such as manganese dioxide,graphite particles, an alkaline electrolyte, and a binder.

Any of the conventional forms of manganese dioxide used for cathodes canbe used. The preferred manganese dioxide is electrolytically-synthesizedMnO₂ (EMD), although chemically-synthesized MnO₂ (CMD), and mixtures ofEMD and CMD can also be used. Distributors of such manganese dioxidesinclude Kerr McGee, Co. (Trona D), Chemetals, Co., Tosoh, DeltaManganese, Mitsui Chemicals, JMC, Evachem, and Chuo Denki. Generally,the cathode includes between about 80% and about 88% by weight ofmanganese dioxide.

The graphite particles act as a conductive aid to increase theelectronic conductivity of the cathode. The graphite particles can beany of the conventional graphite particles used in cathodes. They can besynthetic or nonsynthetic, and they can be expanded or nonexpanded. Incertain embodiments, the graphite particles are nonsynthetic,nonexpanded graphite particles. In these embodiments, the graphiteparticles preferably have an average particle size of less than about 20microns, more preferably from about 2 microns to about 12 microns, andmost preferably from about 5 microns to about 9 microns as measuredusing a Sympatec HELIOS analyzer. Nonsynthetic, nonexpanded graphiteparticles can be obtained from, for example, Brazilian Nacional deGrafite (Itapecirica, MG Brazil (MP-0702X). Generally, the cathodeincludes between about 4% and about 10% by weight of graphite particles.

Examples of binders include polyethylene powders, polyacrylamides,Portland cement and fluorocarbon resins, such as polyvinylidine fluoride(PVDF) and polytetrafluoroethylene (PTFE). An example of a polyethylenebinder is sold under the tradename Coathylene HA-1681 (Hoechst).Generally, the cathode includes between about 0.1 percent to about 1percent by weight of binder.

Cathode 12 may include other additives. Examples of these additives aredisclosed in U.S. Pat. No. 5,342,712, which is hereby incorporated byreference. Cathode 12 may include, for example, from about 0.2 weightpercent to about 2 percent by weight of TiO₂.

The electrolyte solution, e.g., 9N KOH, may be dispersed through cathode12, and the weight percentages provided above are determined after theelectrolyte solution has been dispersed. Generally, the cathode includesbetween about 4 percent to about 8 percent by weight of electrolyte. Insome embodiments, no electrolyte solution is added to the cathode, butthe cathode absorbs electrolyte from other cell components, e.g., theseparator and/or the anode, after the cell is assembled.

Referring to FIGS. 2A–B, interior surface 26 of cathode 12 includesgrooves. As used herein, a “groove” is an elongated channel ordepression on a surface. The cathode 12 can be grooved by removing aportion of a surface of the cathode 12, for example, by turning athreaded tap through the cavity of the cathode 12 to produce a helicalgroove 28 extending about longitudinal axis A of can 18 and cathode 12,as shown in FIG. 2A. Larger threads can be used to remove more cathodematerial and to form larger grooves. The cathode 12 can also be groovedby pushing an appropriately-sized, fluted die through the cathode 12 toform grooves 28 extending parallel to the longitudinal axis A, as shownin FIG. 2B. Vertical grooves can also be formed by sawing (e.g., with ahacksaw) the interior surface 26 of the cathode 12. The grooves can alsobe formed by scratching the surface of the cathode, for example, with adental pick or a wire brush. Grooves of other configurations can also beused. For example, grooves can be wavy, serpentine, zigzagged, ordiscontinuous. Depending on the size of the grooves, different number ofgrooves may be formed, e.g., about 24 to about 72 grooves may be formed.

Alternatively, or in addition, the surface of the cathode 12 can be maderough, for example, by sanding the cathode with 200–400 grit sandpaper.As used herein, “rough” generally means textured, coarse, uneven,irregular, non-uniform, or not smooth. For example, a rough surfacegenerally has unequal ridges and projections. In one method, the surfaceof the cathode 12 can be roughened by using a cathode pellet-formingplunger having a roughened surface that can roughen the inner surface ofthe cathode 12. For example, after the plunger is plunged into a cathodedisc or cylinder to form a ring-shaped disc or hollowed cylinder, theplunger can be twisted radially against the interior surface of theformed disc or cylinder to roughen the disc or cylinder. Once the radialtwist/roughen operation is completed, the plunger is withdrawn from theformed disc or cylinder. Other methods of roughening include, forexample, sand etching, using a pressure nozzle, using a wire brush, andrubbing the cathode with a hard surface.

For AA cells, interior surface 26 of cathode 12 is grooved and/orroughened such that no more than 6% of the original thickness of thecathode is removed, although the amount of cathode removed generallydepends on the starting inner diameter of the cathode. Preferably, nomore than 4.5% is removed, and more preferably, no more than 2% isremoved. Referring to FIG. 2A, the distance between a longitudinal line,e.g., line X, extending along interior surface 26 of cathode 12 and theinterior surface of can 18 preferably remains substantially the samealong the length of cathode 12. As used herein, “substantially the same”means that the distance does not differ by more than 3%. Expressedanother way, grooves 28 can extend beneath the original, unmodifiedinterior surface 26 of the cathode 12 about 10 to about 450 microns,preferably, about 70 to about 110 microns, and more preferably, about 90to about 110 microns. As a result, when a grooved cathode is used in acylindrical alkaline battery, a generally straight-walled cylindricalseparator may be used for the battery even though the interior surface26 of the cathode has been grooved and/or roughened. Generally, tomaintain the maximum amount of active material in the battery, a cathodethat is to be modified by grooving or roughening is provided slightlythicker than an unmodified cathode in order to compensate for the lossof cathode material as a result of grooving or roughening. Methods offorming alkaline cathodes and batteries are known and are described in,e.g., U.S. Ser. No. 09/559,872, filed Apr. 26, 2000, hereby incorporatedby reference in its entirety.

Grooving and/or roughening the cathode 12 increases the surface area ofinterior surface 26. Depending on the size of the grooves, e.g., byadjusting the size of the threads on the die, the apparent surface areaof the interior surface 26 can be increased by more than 100%.

Referring to Table 1, exemplary experimental parameters used to preparegrooved and roughened cathodes for a standard AA cathode are shown. Asused herein, “preshot” is the amount of electrolyte added to the batterybefore the separator is placed, not including the electrolyte alreadyincluded in the cathode pellets.

TABLE 1 Active Internal Groove/Roughen Material Preshot Resistance TestCells Method Loss Added (mΩ) Groove Type I 3/8″ 36 Fine −3.6% +9%, 0%55, 55 Groove Type II 3/8″ 24 Medium −2.6% +6%, 0% 54, 55 Groove TypeIII 3/8″ 16 Coarse −2.2% +5%, 0% 57, 58 Roughened #400 Sand Paper 0 0 56

The resulting grooved-cathode batteries, with or without includingadditional electrolyte, exhibit good performance. Referring to FIGS. 3and 4, two different types of cells with grooved cathodes exhibit goodcapacity under 1 Amp of continuous discharge.

Referring to Table 2, batteries having grooved cathodes generallyexhibit good capacity at high and low drain rates and under continuousand intermittent discharge rates. Generally, the capacity yieldimprovements with grooved cathodes are higher at higher cutoff voltages.The cutoff voltage is the voltage at which a test is terminated because,e.g., the device cannot function at a lower voltage than this cutoff.

TABLE 2 Discharge Capacity Yield (Ahr) Test Regimes Conditions 1.1 V 1.0V 0.9 V 0.8 V 1 Amp Continuous 0.30 0.55 0.81 0.94 1 Watt Continuous0.36 0.58 0.79 0.89 1 Ohm Continuous 0.26 0.60 0.89 1.01 1.1 A(CC-Photo, 10 sec on; 0.40 0.73 1.06 1.40 Flash Camera) 60 sec off 1hr/day 1.8 Ω 15 sec on; 0.67 1.25 1.76 1.96 (IEC Photoflash) 60 sec off0.1 Amp Continuous ? ? ? ?

The strong performance of batteries having grooved cathodes may beattributable to the grooves and/or the increased electrolyte added tothe battery. Grooving the cathode increases the interior surface area ofthe cathode, thereby lowering the current density at the cathodereaction interface, e.g., the cathode/separator interface. Referring toFIG. 5, at an initial period under 1 A, a grooved-cathode batteryexhibits an Ohmic resistance of 52 mV and a kinetic resistance of 45 mV,possibly due to the high surface area at the interior cathode surface.

Increasing the surface area of the cathode may also lower cathodepolarization and curvature effects typically present with cylindricalcathodes. Cathode polarization results from limited diffusion across thecathode/separator interface. When the surface layer of the MnO₂particles is discharged, lower oxides may form which cause increasedpolarization resistance. Grooving or roughening the cathode generateshigher surface area at the reaction interface of the cathode that maygenerate a more uniform current distribution such that, for example, theentire cathode thickness can be discharged at a similar rate, and/or maygenerate a low current density and consequently less voltage drop acrossthe interface. Similarly, grooving a cylindrical cathode may also allowfaster transport of the cell's reactants and products, e.g., by reducingthe cylindrical geometry of the cathode.

Forming the grooves can also improve sorption of electrolyte by openingpores at the cathode surface and/or by modifying the density of thecathode pellets by applying mechanical stresses. Referring to FIG. 6,the effect of the grooves on electrolyte sorption is demonstrated.Measurements were performed by filling the cathode up to the top withelectrolyte and pouring out the electrolyte after different periods oftime. The weight gain by the cathode was measured gravimetrically. Asshown in FIG. 6, the rate of sorption was high in the grooved cathodes.This data indicate that grooved cathodes may induce low mass transferresistance, not only in the cathode but in the separator and anode.Mechanically forming the grooves can also remove highly compact surfacelayers formed by the pelletization and re-compaction process used toform the cathodes.

Generally, increasing the surface area of the cathode, combined withincreasing the amount of electrolyte in the battery, improves the masstransport properties of the battery, i.e., mass transfer resistance islowered and mass flux is increased. Having limited electrolyte generallyincreases the electrode polarization and separator polarization at lowvoltage cutoffs because of high mass transfer resistance and earlieranode passivation. Adding more electrolyte can improve the criticalcapacity yield of a battery, defined as the capacity yield at which theinternal resistance of the cell is drastically increased due toelectrolyte depletion during discharge or during a rest period. Addingmore electrolyte can lower separator polarization, e.g., the voltagedrop across the separator due to ohmic and mass transfer resistance.Adding more electrolyte can also delay passivation of the anode, whichoccurs when hydroxide ions in the electrolyte are depleted. As shown inFIGS. 7A–B, adding more electrolyte to a grooved-cathode battery candelay anode passivation under galvanostatic and galvanodynamicconditions.

Referring to FIGS. 8A–B, the advantage of grooved or roughened cathodesis further demonstrated. FIG. 8A shows that batteries having a roughenedcathode or a grooved cathode, with or without excess electrolyte, inducelow Ohmic and kinetic polarization. Similarly, FIG. 8B demonstrates thatmass transfer polarization is low for roughened or grooved cathodes.Thus, referring to FIG. 9, the overall cell polarization of a roughenedor grooved-cathode battery is low, thereby providing the battery withhigh capacity.

Another possible explanation for improved battery performance is thatroughening or grooving the cathode produces a surface on the cathodethat provides the cathode with better electronic and ionic conduction.Referring to FIG. 10, the graphite particles 30 have a layered atomicstructure in which carbon atoms are bonded in hexagonal arrays arrangedin crystallographic a-b planes. Bonding along the c-direction is mainlyweak bonding, such as from van der Waals or weak covalent bonds.Consequently, electronic conduction in the graphite particles occursmainly in the a-b planes. Also, due to its atomic structure, thegraphite particles generally exhibit preferred orientation, e.g.,graphite particles can be used as lubricants since they generally orientwith their a-b planes parallel to a shearing or sliding force.

Referring to FIG. 11, some methods of forming a cored cylindricalcathode produce a cathode 12 wherein the graphite particles 30 can bepredominantly oriented at random within the bulk of the cathode, hereincalled the “unaffected zone” 32. However, these methods can also producea shiny, glazed, relatively impermeable layer on the inner and outersurfaces of the cathode. Within this layer, herein called an “affectedzone” 34, the graphite particles 30 may be preferentially oriented withtheir a-b planes parallel to the longitudinal axis (A) of the batteryand their crystallographic c-axes perpendicular to axis (A). Sinceelectronic and ionic conduction in cathodes of cylindrical cells aregenerally in the radial direction (R), the orientation of the graphiteparticles in the affected zone 34 may hinder the cell's electronicconductivity, ionic mobility, and electrolyte permeability.

Referring to FIG. 11, grooving or roughening the surfaces of the cathodemay improve the performance of the battery by removing the affected zonecompletely 36 or by removing enough of the affected zone 32 from thesurface layer to approximate the unaffected zone 38. With enoughaffected zone removed, electronic and ionic conduction, as well asliquid permeability, can approach levels reaching those of a cathodehaving no affected zone.

Thus, because conduction in the cathode occurs generally in the radialdirection (R), and because electronic conduction in the graphiteparticles occurs mainly in the a-b plane, it is generally preferred thatthe cathode contain graphite particles having their a-b planes orientedparallel to the radial direction (R). For cylindrical cells, thegraphite particles preferably have their a-b planes perpendicular to thelongitudinal axis A. Preferably, this orientation is maintainedthroughout the cathode and in particular at the cathode's surface, i.e.,at the cathode/separator and cathode/can interfaces, where undesirablepreferred orientation and glazing can occur.

A method of making a cathode for a cylindrical cell having a desiredgraphite particle orientation and which minimizes formation of a glazedsurface will now be described. A fraction, e.g., about 25%, of the totalcathode powder or granulate is placed in a battery can. The can isplaced and supported in a tight fitting die. The cathode powder iscompacted by pressing a compaction plunger into the can to form a solidslug in the bottom of the can. After compaction, the upper surface ofthe slug is essentially perpendicular to the longitudinal axis of thecan. The compaction force helps to orient the a-b plane of the graphiteparticles parallel the radial direction.

The plunger is withdrawn from the can, and an additional fraction ofcathode powder is placed in the can. Compaction with the plunger isrepeated. The above filling and compaction steps are repeated, e.g.,four times, until a desired solid cathode cylinder is formed.

The fractions of cathode powder that are added after the first or secondfraction can also be compacted multiple times to provide a cathodecylinder with uniform hardness. In an exemplary pack and drill method, afirst fraction of cathode powder is placed in the can and compacted orpressed. A second fraction is placed in the can on top of the firstfraction and compacted. A third fraction is placed on top of the secondfraction and compacted twice, allowing the third fraction to relax inbetween compactions. Then, a fourth fraction is placed on top of thethird fraction and compacted three times, allowing the fourth fractionto relax in between compactions. While the bottom fractions (e.g., firstand second) may also experience additional pressures from the multiplecompactions of the top fractions (e.g., third and fourth), generallythese pressures are not as great as the pressures on the top fractions.Thus, this method generally exposes each fraction of cathode material toabout the same compaction pressures so that the formed cathode cylindercan have uniform strength and hardness. It is believed that this methodprovides the formed battery with enhanced storage characteristics.

After the cathode cylinder is formed, the can is removed from thesupport die and secured to a drilling machine, e.g., a lathe. Thecathode cylinder is drilled in one or more passes to form a cathodecavity for the anode. The bottom of the cathode, including a hollowvolume of a pip, may be drilled out, if desired. The method produces acathode with the desired graphite particle orientation and minimizedglazing of the cathode surfaces. This “pack and drill” method cansubstantially orient the graphite particles such that the a-b planes areparallel to the plane of conduction, e.g., parallel to the radialdirection, at the inner diameter, at the outer diameter, and within thebulk of the cathode for cylindrical cells. This orientation facilitatesboth electronic and ionic conduction.

Table 3 shows data for cells having cathodes made by the above pack anddrill method. Generally, batteries made by the above method exhibit goodperformance, particularly at high drain and to high voltage endpoints.

TABLE 3 End Point Voltage → 1.1 V 1.0 V 0.8 V “Pack and Drill” cell0.563 hrs 0.919 1.412

In another variation of the above-described pack and drill method, thecathode material is placed in the can as formed solid pellets ratherthan as granulate. Cathode powder or granulate is pressed into pellets,e.g., each pellet can be formed about 25% of the finished size of thecathode. A first pellet is placed in the can and compacted, e.g., with aplunger. A second pellet is placed in the can on top of the first pelletand compacted. Additional pellets can be added and compacted until thedesired solid cathode cylinder is formed. The cathode may be drilled asdescribed above. The last two pellets are subjected to multiplecompactions, as described above.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, while the above description discusses alkaline cells, theinvention can be applied to other types of batteries, such as metal-airbatteries and air recovery batteries. Similarly, the invention can beapplied to non-cylindrical batteries, such as button cells, prismaticcells, and racetrack cells. The invention can be applied to multi-lobedelectrode batteries, as described in U.S. Ser. No. 09/358,578, filedSep. 21, 1999, hereby incorporated by reference.

The cavity formed by the pack and drill method can be formed by firstforming a smaller cavity, such as by pressing hollow cylinders throughthe cathode or by extrusion, and then enlarging the smaller cavity bydrilling, boring, or abrasion. The cavity may have a non-cylindricalcross section. Orientation of the graphite particles may be aided bymechanical shock applied in the appropriate direction, alternatingmagnetic fields, electrostatic fields, sonic fields, and slip-casting inporous molds.

The invention can be applied to coin cells, button cells, and prismaticcells. In these batteries, the cathode is generally prismatic, e.g., acircular prism or a rectangular prism. Referring to FIGS. 12 and 13,electronic and ionic conduction in these cells generally flow parallelto the major axis A of the cathodes 12 or perpendicular to the majorsurface of the cathodes. As used herein, the major surface is thesurface perpendicular to the major axis. Thus, the graphite particlesare preferably oriented with their a-b planes parallel to the cells'longitudinal axes. The cathodes for these cells may be formed bycompacting a block of cathode material and then cutting slices ofcathode from the block such that the a-b plane of the graphite particlesare parallel to the cells' longitudinal axes when the cathode is placedin the cell.

For cathodes having a current collector, such as a screen or foil,conduction generally occurs mainly perpendicular to the major surface ofthe current collector. The active material, graphite particles, andbinder may be electrostatically deposited on the current collector toprovide the desired orientation, i.e., the a-b planes of the graphiteparticles are perpendicular to the major surface of the currentcollector, and then the binder is cured to maintain the desired graphiteparticle orientation.

Other embodiments are within the claims.

1. A battery, comprising: a housing; an anode; a cathode disposed withinthe housing, the cathode comprising: an exterior surface alignedsubstantially parallel to a longitudinal axis and adjacent the housing,a longitudinally-extending cavity defined at least in part by aninterior surface but not by the exterior surface, manganese dioxidebetween the interior surface and the exterior surface, and at least onegroove extending about 10 microns to about 450 microns into the interiorsurface of the cathode; and a separator between the anode and thecathode, wherein a cross-sectional area of the separator relative to thelongitudinal axis is circular.
 2. The battery of claim 1, wherein theseparator is a circular cylinder.
 3. The battery of claim 1, wherein thecathode is shaped as a cored cylinder having the interior surface andthe exterior surface.
 4. The battery of claim 3, wherein the grooveextends parallel to the length of the cathode.
 5. The battery of claim1, wherein the groove extends about 70 microns to about 110 microns intothe interior surface of the cathode.
 6. The battery of claim 1, whereinthe groove extends about 90 microns to about 110 microns into theinterior surface of the cathode.
 7. The battery of claim 1, wherein thehousing has a length, and a cross-sectional area of the separatorrelative to the longitudinal axis is essentially uniform and extends forsubstantially the entire length of the housing.
 8. The battery of claim1, wherein the groove extends parallel to the longitudinal axis of thebattery.
 9. The battery of claim 1, wherein the battery is cylindrical.10. The battery of claim 6, wherein the housing has a length, and across-sectional area of the separator relative to the longitudinal axisis essentially uniform and extends for substantially the entire lengthof the housing.
 11. The battery of claim 9, wherein the battery is a AAbattery.
 12. The battery of claim 9, wherein the battery is a AAAbattery.
 13. The battery of claim 9, wherein the battery is a AAAAbattery.
 14. The battery of claim 9, wherein the battery is a C battery.15. The battery of claim 9, wherein the battery is a D battery.
 16. Thebattery of claim 1, further comprising an aqueous electrolyte.
 17. Thebattery of claim 1, further comprising an alkaline electrolyte.
 18. Thebattery of claim 17, wherein the alkaline electrolyte comprisespotassium hydroxide.
 19. The battery of claim 1, wherein the battery isan alkaline battery.
 20. The battery of claim 1, wherein the cathodecomprises multiple lobes.
 21. The battery of claim 1, wherein themanganese dioxide comprises electrolytically-synthesized manganesedioxide.
 22. The battery of claim 1, wherein the cathode comprisesbetween about 80% and about 88% by weight of the manganese dioxide. 23.A cathode comprising: at least one groove extending about 10 to about450 microns into a surface of the cathode; and a transition metal oxide,wherein the cathode is shaped as a cored cylinder having an interiorsurface and an exterior surface, wherein the groove extends into theinterior surface of the cathode, and wherein the groove extendshelically about the longitudinal axis of the cathode.
 24. A batterycomprising: a cathode having at least one groove extending about 10 toabout 450 microns into a surface of the cathode; and a transition metaloxide, wherein the groove extends helically about the longitudinal axisof the battery.
 25. A battery comprising: a housing; and a cathodedisposed within the housing, the cathode comprising: an exterior surfacealigned substantially parallel to a longitudinal axis and adjacent thehousing, a longitudinally-extending cavity defined at least in part byan interior surface but not by the exterior surface, a transition metaloxide between the interior surface and the exterior surface, and atleast one groove extending about 10 to about 450 microns into theinterior surface of the cathode, wherein the battery is a metal-airbattery.
 26. The battery of claim 25, wherein the groove extends about70 to about 110 microns into the surface of the cathode.
 27. The batteryof claim 25, wherein the groove extends about 90 to about 110 micronsinto the surface of the cathode.
 28. A battery comprising: a cathodehaving at least one groove extending about 10 to about 450 microns intoa surface of the cathode; and a transition metal oxide, wherein thebattery is an air-recovery battery.
 29. The battery of claim 28, whereinthe groove extends about 70 to about 110 microns into the surface of thecathode.
 30. The battery of claim 28, wherein the groove extends about90 to about 110 microns into the surface of the cathode.